Self-contained breathing apparatuses (SCBAs) can be very useful in providing breathable air to users, such as astronauts, firefighters, rescue workers, etc., in hostile environments for breathing. SCBAs can also be very useful in providing breathable air in extraterrestrial environments, including the moon, Mars, asteroids, and other environments in space. Return of conditioned breathable air may be critical in potential Immediately Dangerous to Life and Health (IDLH) or Biological, Radiological, and Nuclear (CBRN) environments. Closed-loop SCBAs may remove carbon dioxide from exhaled breath, and recirculate the exhaled breath back to the user by supplementing the exhaled breath with oxygen. Closed-loop SCBAs may provide a long-duration supply of conditioned breathing gas to the user.
State of the art closed-loop SCBAs typically rely on a chemical sorbent to remove carbon dioxide from exhaled breath, performing a function in reconditioning the flow for inhalation. The chemical sorbent may release water and heat as a byproduct of the chemical reaction with carbon dioxide. Heat and water generated by carbon dioxide sorbents found in SCBA systems, including in off-the-shelf SCBA systems, can result in dangerously high return temperatures and undesirable condensation in the SCBA systems. Increased heat and humidity in recirculated air may also adversely affect user comfort during breathing. Closed-loop SCBAs may integrate heavy ice or other phase change materials to provide sensible cooling. However, these cooling systems are not only heavy but their effectiveness can be short-lived and severely limit the use duration in warm to hot environments. These cooling systems are heavy, logistics-intensive, and quickly expended depending on the environment that the SCBA is operated in. Conventional exchange and energy storage units may not be applicable with high-performance chemical sorbents, such as soda lime and lithium hydroxide, which react to form water. The water may condense and limit the ability of such conventional exchange and energy storage units from performing bulk heat exchange.